Accustomed to being badly ruined (6)
I believe the answer is:
inured
'accustomed to' is the definition.
(I've seen this in another clue)
'badly ruined' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'ruined' with letters rearranged gives 'INURED'.
'being' is the link.
(Other definitions for inured that I've seen before include "Hardened, maybe ruined" , "Accustomed to something difficult" , "Hardened, perhaps ruined" , "Hardened as by experience" , "Habituated or hardened" .)